1. Field of the Invention
The present invention relates to an electric energy storage device and more particularly, to an electric energy storage device having a large capacity and including an electrode group manufactured by winding into a plate shape in order to facilitate an electrode integration and the manufacturing of the electric energy storage device.
2. Description of the Related Art
Recently utilizing electric energy storage device includes a battery, an electrolytic condenser, electric double layer capacitor, pseudo capacitor, etc. In particular, an electric chemical capacitor attracts much concern as an auxiliary energy storage device in a hybrid electric device into which the electric power is supplied by a rechargeable condenser. The electric double layer capacitor (EDLC) is a capacitor utilizing a constant charge phenomenon generated from an electric double layer formed at an interface between different phases.
FIG. 1 is a schematic diagram of a unit cell of a conventional and common electric energy storage device such as a battery and a capacitor. The unit cell of the conventional electric energy storage device includes a case 10 formed from a metal or a molded resin, electrodes of a cathode and an anode which are composed of a current collector 12 and active material layer 14, a separator 15 of a porous material provided between the cathode and the anode, to allow an ion conduction while preventing an electron conduction and an electrolyte 18 filled in case 10.
Active material layer 14 is an electric energy storing portion and different materials are utilized according to the type of the electric energy storage device. Current collector 12 discharges out the stored energy of active material layer 14 or transmits an externally applied electric energy to active material layer 14. Usually, current collector 12 is manufactured as a metal layer. However, aluminum electrolyte condenser includes a metal layer obtained by etching aluminum and then forming an aluminum oxide layer thereon. In this case, the active material layer and the current collector are not differentiated.
Separator 15 is provided between the cathode and the anode, to allow an ion conduction while preventing an electric conduction. A porous polypropylene or paper is widely used as separator 15. Electrolyte 18 is prepared by dissolving ion into a solvent so as to store an electric energy. Various electrolytes are utilized according to the type of the active material.
The storing amount of the electric energy per weight/volume of the electric energy storage device including the battery, electrolytic condenser, electric double layer condenser, etc. is determined by the types of the active material. Accordingly, in order to increase the capacity of a unit package, the amount of the active material should be increased. When the thickness of the active material layer of the electrode is increased, the area of the electrode can be decreased, however, the electric resistance of the electrode increases and the efficiency of the active material decreases. Thus, the increase of the thickness of the active material layer is limited.
Recently, an electric energy storage device having a large capacity is manufactured by thinning an active material layer while enlarging the area of an electrode.
FIG. 2 is a perspective view of a conventional electric energy storage device for showing an integrated state of electrodes of a hexahedral shape. FIG. 3 is a cross-sectional view of the electrode illustrated in FIG. 2 cut along a line Axe2x80x94Axe2x80x2 for schematically showing the integrated state of the electrodes.
Referring to FIGS. 2 and 3, cathodes 20a and 20b and an anode 22a which have square shapes are separated by separators 24a and 24b and they are integrated. At one side of each anode 20a and 20b and cathode 22a, a lead line is formed for a connection to terminals of cathode and anode. The lead lines are formed to respectively collect them into two groups having opposite directions according to their polarities.
Since the integrated state of the electrodes makes a hexahedron, the electrode is called a hexahedral shaped electrode.
FIG. 4 is a perspective view of a conventional electric energy storage device for showing an integrated state of electrodes of a cylindrical shape.
Referring to FIG. 4, since each electrode is wound and integrated into a cylindrical shape, the electrode is called to have a cylindrical shape. A plurality of cathodes 30a and 30b and a plurality of anodes 32a and 32b are integrated and are separated by separators 34a and 34b. At one side of each cathode 30a and 30b and anode 32a and 32b, a lead line is formed for a connection to terminals of a cathode and an anode. The lead lines are respectively collected into two groups according to their polarities.
For the hexahedral or cylindrical electrodes illustrated in FIGS. 2 and 4, some methods for manufacturing the lead lines and connecting them to the terminals are as follows. The lead lines can be manufactured by cutting the current collector, or the lead lines can be manufactured and connected to the terminals by molding onto the electrode. A method of fixing the lead lines by utilizing a rivet or a press, etc. can be exemplified.
However, for the hexahedral electrode, the integration of the electrodes are implemented as follows. First, the electrodes are cut into square shapes and the electrodes are integrated while inserting the separators between the cathodes and the anodes. Then, the cathodes of the electrodes are connected to the terminal of the cathode and the anodes are connected to the terminal of the anode. When the integration number of the electrodes increases, much time is taken and the reliability of the product is deteriorated.
For the cylindrical electrode, the lead lines are formed at the electrodes with a predetermined distance and the electrodes are wound into a cylindrical shape. Then, the lead lines are connected to the terminals of the cathode and the anode. When the number of the lead lines is small, this procedure is simple. However, when the number of the lead lines increases, the procedure is complicated.
For an electric energy storage device having a large capacity, currents having hundreds of amperes flow during charging/discharging. Therefore, a large number of lead lines is needed. This will decrease an electric resistance and so the increase of the number of the lead lines is advantageous for applying current of a high value.
However, for the cylindrical electrode, the increase of the number of the lead lines results in a complicated procedure for cutting a portion of an element to manufacture the lead lines or for manufacturing the lead lines. In addition, the adjustment of the positions of the cathodes and the anodes during the winding of the electrodes into the cylindrical shape also becomes difficult.
Accordingly, it is an object in the present invention to provide an electric energy storage device having a large capacity and a large number of lead lines, in which the integration of the electrodes is simple and reliable.
To accomplish the object, there is provided in the present invention an electric energy storage device comprising at least one electrode group in which a cathode, a separator and an anode are in regular sequence, repeatedly integrated and wound into a plate shape. The electrode group has lead lines collected at a predetermined position for a connection with a terminal.
The lead lines can be formed by cutting each side of the cathode and the anode before integrating the cathode, anode and separator into a plate shape or preferably, by cutting one side of the cathode and anode after integrating them.
Preferably, a plurality of the electrode groups are integrated with an insertion of a separator between the electrode groups to accomplish the large capacity of the device. The electric energy storage device further comprises a case for including the plurality of the integrated electrode groups and an electrolyte filling up the inside of the case.
According to the present invention, the integration of the electrodes and the formation of the lead lines from the electrodes are very advantageous. Therefore, the manufacture of the electric energy storage device having a large capacity is very advantageous.